There is no way you can convert a C++ app into C#. The Problem here is C# is not like C++, the syntax might look the same somewhere , but it does not work the same.

You need to understand the functionality that is written in C++ and then rewrite it in C# , the thing here is that you will have a challenge if you cant read C++ Code. but Telerik Created a VB.NET to C# and virsa versa i am sure there are other tools that can do that like these